Home Range and Habitat Utilization of Breeding Male Merlins,
Falco columbarius, in Southeastern Montana
DALE
M.
BECKER1,2
and CAROLYN HULL SIEG3
1
USDI Fish and Wildlife Service, Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, Montana
59812
2
Present Address: USDI Bureau of Indian Affairs, Flathead Agency, Box A, Pablo, Montana 59855
3
USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, South Dakota School of Mines Campus,
Rapid City, South Dakota 57701
Becker, Dale M., a n d Carolyn H
columbarius, in southeaster
1 Sieg. 1987. Home range and habitat utili zation of breeding male Merlins, Falco
Monta na. Canadian Field-Naturalist 10l(3): 398-403.
Home range size and habitat utilization of three breeding male Richardson’s Merlins (Falco columbarius richardsonii) in
2
southeastern Montana were studied using radio telemetry. Home ranges of these birds encompassed 13,23, and 28 km . Each
bird traveled up to 9 km from its nest. Each home range encompassed five habitats; sagebrush/grassland, riparian, and
Ponderosa Pine (Pinus ponderosa) communities were used significantly (p 5 0.05) more, and grasslands and agricultural
fields less (p 5 0.05), than expected, based on the proportions in the combined home ranges. Four sites regularly used by
hunting male Merlins indicated preferences for patchy shrub/grasslands as hunting habitats.
Key Words: Merlin, Falco columbarius, home range, habitat, southeastern Montana.
Richardson’s Merlin (Falco columbarius
richardsonii) is an inhabitant of sparsely treed grasslands in
the northern Great Plains. Breeding pairs in Canada
nest in small groves of deciduous trees along rivers
(Bent 1938) and shelterbelts adjacent to grasslands
(Hodson 1976). In the western United States,
Richardson’s Merlins nest in deciduous riparian
communities (Call 1978) and in coniferous stands in
close proximity to grasslands (Ellis 1976; Becker
1984).
Previous food studies in these areas suggest that
Richardson’s Merlins hunt in grassland habitats (Bent
1938; Fox 1964; Hodson 1976); however, detailed
information on habitat utilization and home ranges of
these birds is lacking in the literature. The objectives
of this study were to determine the size of home ranges
of male Merlins and to identify preferred hunting
habitats. Males were selected for study because they
do most of the hunting for the breeding pair and
nestlings.
Study Area
The 39 448-ha study area in southeastern Montana
consisted largely of sagebrush/ grassland shrubsteppe and agricultural fields interspersed with buttes
and rolling hills dominated by stands of Ponderosa
Pine (Pinus ponderosa). Maximum elevation is
1282 m above sea level. The climate is characterized
by hot summers, cold winters, and a semi-arid
moisture regime. Annual precipitation averages
39 cm, of which 70% falls from May through
398
September. Monthly mean temperatures during the
Merlin breeding season range from -8 o C in March to
33oC in July.
Methods
Adult male Merlins were captured near their nest
sites in late May and early June of 1980. To minimize
disturbance of breeding adults near their nests,
capture was attempted only after young had hatched.
A dho-gazza trapping device was modified from that
described by Beebe and Webster (1964), and a
permanently crippled Great Horned Owl (Bubo
virginianus) was used to lure the Merlins into mist
nets. After capture, the Merlins were restrained in a
stocking while the transmitters were being attached.
Each of the three male Merlins captured was fitted
with an SM-1 transmitter manufactured by the AVM
Instrument Company 1 The transmitter package
weighed approximately 7 g, or approximately 4 % of
the bird’s weight. It was attached ventrally to the
proximal end of the shaft of a central tail feather by
two strands of monofilament embedded in the dental
acrylic covering of the transmitter package. Antennas
1987
BECKER
AND
SIEG:
HOME RANGE
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HABITAT
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MALE MERLINS
401
TABLE 2. Percent bare ground, litter cover, and plant canopy cover of major plant species on four sites where male
Richardson’s Merlins were frequently observed hunting in southeastern Montana.
Site number
Cover Type
1
2
3
4
BARE GROUND
42.5
18.9
18.4
9.3
LITTER
S HRUBS
Silver Sagebrush, Artemisia cana
Fringed Sagebrush, A. frigida
Big Sagebrush, A. tridentata
Plains Pricklypear, Opuntia polyacantha
Woods Rose, Rosa woodsii
Western Snowberry, Symphoricarpos occidentalis
1
OTHERSHRUBS
GRASSES
Western Wheatgrass, Agropyron smithii
Blue Grama, Bouteloua gracilis
Buffalograss, Buchloe dactyloides
Sandberg Bluegrass, Poa secunda
2
Other grasses
FORBS
Common Y arrow, Achillea millefolium
3
Other forbs
8.9
16.4
19.8
29.6
0.6
19.3
1.1
0.1
11.7
0.7
1.1
7.4
0.6
O THER
Lichen, Parmelia chlorochrae
Club Moss, Selaginella densa
Algae
10.4
0.2
1.2
16.3
1.0
1.0
1.3
6.4
2.1
1.3
0.5
1.0
2.6
13.7
5.3
8.2
2.0
1.1
1.3
2.3
1.0
1.9
5.3
2.6
16.1
0.5
1.0
2.2
26.4
2.5
1.0
1.9
2.5
10.6
0.8
1
Gardner Saltbush (Atriplex gardneri), Broom Snakeweed (Gutierrezia sarothrae).
Tumblegrass (Schedonnardus paniculatus), Needle and thread (Stipa comata).
Small-leaf Pussytoes (Antennaria parvifolia), thistle (Cirsium sp.), Scarlet Gaura
(Gaura coccinea), Silky Crazyweed
(Oxytropis sericea), Fuzzytongue Penstemon (Penstemon eriantherus), Scurfpea
(Psoralea
sp.), Field Pennycress (Thlaspi
arvense), Hoods Phlox (Phlox hoodii).
2
3
(Table 2). Site 3 was dominated by Big Sagebrush and
Western Wheatgrass. Each of these three sites were in
the sagebrush/grassland habitat. Site 4 was in the
riparian habitat, and was dominated by Western
Snowberry and Western Wheatgrass.
Shrub densities in the three sagebrush/ grassland
sites were variable, ranging from 7530 to 14740 stems/
ha of Big Sagebrush and Gardner Saltbush (Atriplex
gardneri) (Table 3). The riparian site had a total shrub
density of 43350 stems/ha. Average maximum
vegetation height was also variable, averaging 16.6 cm
on the three sagebrush/grassland sites, and 44 cm on
the riparian site.
Discussion
Few comparative data on home range sizes or
foraging distances of breeding Merlins are available.
Hodson (1976) concluded from behavioral observations that breeding Merlins in Alberta hunted up to
1.6 km from their nesting sites. The home ranges of
the Montana Merlins and maximum distances they
traveled from their nests were considerably larger.
Richardson’s Merlins have longer wings and tails and
lighter wing-loading in comparison with other
subspecies of Merlins inhabiting forested habitats.
These physical differences may be adaptations that
allow this subspecies to range over large areas
(Temple 1972). Other factors involved in these
differences may have included differences in habitats
within home ranges, terrain, prey availability and
abundance, or some combination of these factors.
Results of this study indicated a high degree of use
of sagebrush/ grassland habitats by hunting male
Merlins during June and July. A study of food habits
of this population of Merlins indicated that Horned
Larks (Eremophila
alpestris),
Lark Buntings
(Calamospiza melanocorys), and Vesper Sparrows
(Pooecetes gramineus) constituted
27%, 18%, and
13% of 427 food items, respectively (Becker 1984).
Merlin use of sagebrush/grassland may have been a
402
T HE
CA N A D I A N
TABLE 3. Shrub densities (stems/ ha) at four sites where
hunting male Richardson’s Merlins were frequently
observed in southeastern Montana.
Shrub densities (stems/ ha)
Site number
Species
Big Sagebrush
Western Snowberry
Silver Sagebrush
Woods Rose
Gardner Saltbush
Totals
2
3
14740 7 110 4470
- 35
5
- 2
420
20
14 740 7 530 4 490 43
4
130
590
540
090
350
direct result of relatively high densities of Horned
Larks and Vesper Sparrows drawn to food, cover, and
elevated perches provided by Big Sagebrush
interspersed with grassland.
Male Merlins were observed less often in grasslands
than expected, based on availability of this habitat. In
contrast,
food habits of breeding Merlins in
southeastern Montana indicated that birds typically
associated with open grassland habitat were heavily
preyed upon (Becker 1984). Similar results have been
reported by Fox (1964) and Hodson (1978) for
Merlins in Canada. The importance of the grassland
habitat in our study, as represented by the number of
radio locations in it, may have been underestimated
because of a lack of elevated hunting perches in the
form of shrubs or because of difficulty in locating
Merlins perched on the ground in broken terrain.
Thus, grassland habitat may be more important to
hunting Merlins than indicated by the data presented.
The limited use of agricultural habitat by adult male
Merlins might have been influenced by a lack of
perching sites, difficulty in locating Merlins on the
ground, or by lower vegetation diversity and a
corresponding lower density of potential prey species.
In a study of avian habitat use in central North
Dakota, Horned Larks and Vesper Sparrows were
two of the most common species observed in
croplands; however, of all major habitats sampled,
croplands had the lowest breeding bird populations
(Faanes 1982). The limited use of croplands by
breeding birds was further illustrated by lower species
richness, mean density, and species diversity in the
North Dakota study.
Higher than expected use of riparian habitats by
hunting male Merlins was attributed mainly to the
presence of water and food sources that attracted prey
species. Also, shrub cover in this habvitat likely
provided perches for both Merlins and their prey.
The Ponderosa Pine habitat probably is not an
important hunting habitat for Richardson’s Merlins.
F I E L D -N ATURALIST
Vol. 101
Forest avifauna constituted only 7% of food items
identified for this population of Merlins (Becker
1984). However, because nests of the three Merlins in
this study were in Ponderosa Pine stands, the birds
spent considerable time at or near nest sites between
hunting forays.
The patchy shrub cover on four sites regularly used
by hunting male Merlins likely provided cover,
nesting sites, and perches for prey species. The variety
of plant species on these sites may also have provided
excellent food sources for passerines. In addition,
small depressions in the ephemeral stream bed on the
riparian site held water during the entire study period,
and was likely important in attracting prey species.
Although shrub density was highly variable on sites
where Merlins were regularly observed hunting, it
appeared that the presence of some shrubs increased
the use of the site by Merlins. Shrubs were probably
important to resident birds for elevated singing
perches, as well as for hiding and nesting cover. The
high variability in shrub densities and heights likely
contributed to a diverse prey base. For example,
Horned Larks make greater use of sites with low shrub
densities, whereas Lark Buntings and Vesper
Sparrows are more apt to utilize sites with
intermediate to higher shrub densities (Johnsgard
1979).
The results of this study indicated that Merlins used
diverse habitat and prey; however, they relied most
heavily on the abundant avifauna of sagebrush/
grasslands of the shrub-steppe. Management
activities that would maintain or increase the natural
diversity of these habitats would be beneficial to both
Merlins and their prey. Removal of shrubs or
conversion of sagebrush/ grassland habitat to
agricultural cropland could reduce the quality of
Merlin hunting habitat. The importance of the
Ponderosa Pine habitat on the study area was clearly
indicated by the Merlins’exclusive use of this habitat
for nesting (Becker 1984). The pine community also
provided important perching and roosting sites. Thus,
management efforts in the area should be aimed at
maintaining Ponderosa Pine and adjacent sagebrush/
grassland habitats.
Acknowledgments
We gratefully acknowledge assistance with field
work by D. W. Carney and R. LeVesque. C. M.
Anderson, I. J. Ball, M. R. Fuller, and C. W.
Servheen provided critical review of earlier drafts of
the manuscript. Funding for the study was provided
by the USDA Forest Service, Rocky Mountain Forest
and Range Experiment Station at Rapid City, South
Dakota.
1987
BECKER
AND
SIEG H O M E R ANGE
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H ABITAT
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Received 6 November 1985
A c c e p t e d 24 August 1987